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More Water vs. Foam
Comparisons

This week we wanted to
fly a couple of verification tests after seeing the improvements
in flights with foam at the last launch. Because of the
uncertainties from the last launch about the actual pressure
used, for these tests we set the pressure to 120psi once and
then launched all the flights with that one setting. We used the
same rocket and setup as last time, with the same amount of
water.

The first launch was a repeat of the standard 9mm nozzle and
water only. The rocket went vertical and reached an altitude of
361 feet (110m) which closely agreed with the previous flights
and also with the simulated results.

We then flew the rocket with a full-bore nozzle and no launch
tube. We wanted to eliminate the effects of launch tubes for
this test. The rocket went to 403 feet (122m) which also closely
matches with a simulator prediction of 403 feet.

We then repeated the test with a 9mm nozzle and added foam
to the measuring jug and filled it until we had 1.5L. This way the
same amount of liquid was added by volume to the rocket. This time the rocket
went up to 494 feet (150m) which was 130 feet higher than water
alone and was another 30 feet higher than the same flight at the
last launch.

We repeated the experiment with a full bore nozzle adding foam to the water. We didn't think that foam would offer much
performance boost in this case due to the large nozzle and short
duration burn. We
were surprised to find that the rocket went up to 535 feet.
(163m) again this was a significant boost over water alone.

So in conclusion foam seems to add significant boost in
altitude for this rocket configuration.

On launch #4 the parachute deployed just after
launch. The rocket was using the full bore nozzle so it was
going quite fast. The shock cord and parachute withstood the
force and brought the rocket back safely. There was only minor
nosecone fairing damage which we just popped back out. The
rocket only flew to 63 feet (19m). On video
review of the launch it was evident that half way through
pressurisation the timer triggered but the guide rail held the
parachute door closed but we could not see this from our position.
The reason the timer triggered was simply because the break-wire
cord was too tight. This was because the Clark cable-tie
launcher extension we put on the launcher moved the entire
rocket further up and we forgot adjust the length of the cord. When we
powered up the timer everything was fine, until the rocket
started stretching when pressurising and this finally triggered
the timer. The break-wire is loosely twisted together so any
tension
could have caused the trigger. Next time we'll make sure there
is more slack in the break-wire cord.

Results Summary

Flight

Water

Nozzle

Altitude

1

1500mL

9 mm

361' / 110m

2

1500mL

22 mm

403' / 122m

3

1470mL + 30mL foam

9 mm

494' / 150m

5

1470mL + 30mL foam

22 mm

535' / 163m

Polaron G2 Launcher Tests continued...

We brought along the G2 launcher to test the
synchronization using the 2ms step increments. All three air
only tests
went well.

We then attached a short fill tube to one of the
booster nozzle seats and filled one of the bottles 1/3 full of water. This
was the first wet test for the launcher. The slow-mo video
showed that although the bottle was released just ahead of the
others, due to the weight it was soon overtaken by the air only
bottles. Once we have the full rocket on there, the acceleration
will be even lower making the timing just a little
less critical.

Ready for sync test

Adding drag and weight to
reinforced bottle

Ready to launch

Next we wanted to test the release heads at 200psi. For this
we brought a fiberglass reinforced 90mm spliced-pair. We then
tested each of the release heads one at a time by disconnecting
the hoses from the air manifold and directly connecting them to
the air inlet hose. To stop the bottle flying up too high and
potentially getting damaged, we draped a towel over the top to
provide weight and drag. We pressurised to 200psi with air only and held
it for a short time before launching to verify the hold down, as
well as the release. All four release heads passed the test. More details are available on the
G2 build log.

No worries

200psi air only test

Testing with fill tube and water

Next we will shift focus back to the rocket and boosters in
particular. We needed to get the launcher done first so that we
can mount the booster retention mechanisms. Their position was
dependent on how the rocket would sit on the launch pad.